It would be a pretty useful skill, but can you really tell the sex of a cannabis seed by just looking at it? Hydroponic Marijuana Sexing Marijuana sexing simply means determining the gender of your marijuana. While cannabis occasionally may be hermaphroditic (having both pistils and stamens), generally, Learn how to find tiny pre-flowers at the base of each leaf to determine the sex of your plant in the vegetative stage (at only 3-6 weeks from germination)!
Can You Tell The Sex Of Cannabis Seeds?
For those who don’t use feminized seeds, being able to tell the sex of a cannabis seed by looking at it would be a pretty handy skill. But is it possible?
If you are a veteran of the cannabis community, or spent a lot of your time reading up on cannabis, you may have heard that it is possible to tell the sex of cannabis seed simply from its appearance. There is even a chart floating about out there that describes the physical differences between male and female seeds.
Well, let us tell you now, it is all a load of bollocks. There is no way to tell the difference between male and female cannabis seeds by looking at them. In fact, it is widely accepted that the sex of a cannabis plant is not determined until a few weeks before flowering.
Even feminized seed, which have been bred to have 99.9% chance of growing female, can turn into male or hermaphrodite plants if put under a ton of stress while growing. This is very rarely a worry for feminized growers, as they don’t tend to stress out their plants to this extreme extent – but it is possible.
Think about it. Why would breeders across the globe go to all the effort required to produce feminized cannabis seeds if they could simply look at regular cannabis seeds and categorize them? It isn’t some conspiracy or well-kept trade secret.
DETERMINING THE SEX OF YOUR CANNABIS BEFORE IT COMES A PROBLEM
While being able to determine the sex of a cannabis seed by looking at it is a myth, being able to sex your cannabis early isn’t.
Normally, you would wait until your cannabis plants are done with vegetative growth, and switch them over to flowering. You then watch like a hawk for any signs of sex, and move the males as soon as possible. This is risky, though, because if you leave it too long, you risk the chance of pollination – turning your bud into seeds. Unless you are getting into breeding yourself, this is something you probably want to avoid.
If you don’t want to take the risk, then sexing your cannabis early is pretty easy, and stress-free. It basically involves placing a black bag over a small section of the plant during the vegetative stage to force pre-flowering, before allowing it to revert back. This gives you a clear idea of what sex your plants are, without undue worry, wasted time, or effort.
It is a sad truth that you cannot determine the sex of a seed by looking at it. If you think you can, you have been lucky. Nothing more. However, hopefully, our explanation of the measures you can take to determine the sex of your cannabis plants will help you keep your grow room male free for years to come!
Hydroponic Marijuana Sexing
Marijuana sexing simply means determining the gender of your marijuana. While cannabis occasionally may be hermaphroditic (having both pistils and stamens), generally, plants are wholly male or female. After four or five weeks you will start to have a chance at sexing the plants. Although generally considered one of the trickiest parts of growing your own marijuana. Marijuana sexing is quite straightforward and will become easier as you gain more experience. The reason for sexing your plants is so that you can remove male plants before they have a chance to pollinate the females. If this occurs the females will start to develop seeds and this will divert their energy from THC production. Which if course is not cool. Left to their own devices plants will develop pre-flowers after around 4 – 6 weeks. This is the right time to remove the males and commence the flowering stage. Marijuana is a dioecious plant which simply means that the males will produce pollen and the females will produce seeds. Although, as in other forms of life, hermaphrodites do occur. Unless you are a breeder or otherwise growing for seed stock, it is preferential to have all female plants as it is the unfertilized calyx or buds which are the most psychoactive and potent part of the plant, the THC, CBN and CBD. So your seedless buds (sinsemilla) are the most preferred harvest for smoking as no energy or weight has gone into making seeds. Therefore, to use energy, time and space on male plants is wasteful of limited resources; thus they should be identified as early as possible and either segregated (for breeding) or destroyed before they release their pollen. Occasionally marijuana will show pre-flowers (immature indicators of the sex of the plant) while still in the vegetative state, but generally require the shift to the flowering phase (shortening the light regimen to 12/12 – 12 hours of light and 12 hours of total dark).
Flowering is the only true way to sex your plants
Although you may get a clue from their growth patterns before flowering. Male cannabis plants tend to be leggier than female plants with a longer internodal length. Female plants are squatter with more leaves and a bushier aspect. Male pre-flowers should be clearly visible to the eye, although a magnifying glass will make your job easier. Male flowers form at the junctions of the branches and stem and the pollen sacs form little balls. Female pre-flowers will also form at the junction of branches and stem but will normally start to form at the fourth or fifth branches up from the base. They are easily distinguished by the appearance of pairs of tiny white hairs, known as pistils. Some growers force flowering by changing the light cycle before the appearance of pre-flowers. They then watch their plants closely for the appearance of flowers and remove the males. However, others believe that this can stress the plants and is not a proven way of speeding up the process as plants forced in this way may spend longer in the flowering phase, cancelling out the advantage.
A magnifying glass is helpful though not necessary. Look near the top branches right where they fork from the stalk. The male sex organ will look like a small playing card-type club. The female sex organ will display a calyx with two small white hairs protruding from the top. If you are unsure or unable to determining the sex, then simply wait a few more days until the organs are more mature and easier to identify. The males are still way too young to create pollen so there is no danger in waiting.
- Force flowering by putting the plant under 12/12 light cycle. The drawbacks of this are that two separate rooms or grow spaces are required. More importantly the plant gets hormonally confused being switched between vegging to flowering, then back to vegging and finally flowering once again. This method allows you to cull your males early, but most likely will delay your harvest for a few weeks.
- Cover a lower branch with black plastic cut from a garbage bag. Do not use a thin bag that allows light to pass through. This must be put on every 12 hours and removed every 12 hours at the same time. The branch will show its sex long before the rest of the plant while still allowing it to ‘veg’ otherwise normally.
Occasionally a plant will exhibit both sexes. This usually occurs when a female plant is late into flower and remains unpollenated. In a last ditch effort to create seeds, marijuana plants have an emergency back-up plan: they sometimes create a small number of male flowers in an attempt to pollinate themselves. Some growers pinch off the few visible ‘bananas’; others may remove and/or destroy the plant so as not to pollenate a whole crop. Marijuana sexing is not difficult once you familiarize yourself with some basic plant physiology.
Cloning marijuana is a great method to use as all shoots are genetically identical to the parent. Thus if you find a donor parent plant that you like (one with desirable genetic traits) and is large and healthy enough to remove branches for cuttings, you may skip the whole sexing ritual as they are 100% the same sex as the parent.
Feminized marijuana seeds
These are a relatively new phenomenon on the cannabis culture scene, and while looked down upon by some old-timers, purists and large-scale growers, are a great boon to the small grower with limited space and time. It is currently not possible to tell the sex of a cannabis seed by examining it (though many untested myths abound), but the mix of males and females is roughly half and half. The larger the amount of seed purchased and/or planted, the closer the ratio will be to 50%. However, if you purchase a small quantity such as five seeds, it is possible to get all males, all females or any mix in between. Feminized marijuana seeds are not foolproof nor 100% guaranteed, but ratios of 90%+ female are quite common.
Cannabis Pre-Flowers: Identify Sex of a Plant as Early as 3 Weeks Old (with pics!)
The female plants will soon produce pistils. Wispy white hairs are a sure sign that you’re looking at female pre-flowers.
How to Determine the Sex of a Young Cannabis Plant
What are cannabis “pre-flowers?” They are little versions of adult flowers that appear on your marijuana plants relatively early in the vegetative stage.
When I first started growing weed, I learned (incorrectly) that there is no way to determine a cannabis plant’s sex until the flowering stage. But I’ve since learned that pre-flowers can reveal the plant’s sex while it’s still in the vegetative stage! Cannabis plants grow pre-flowers as young as 3-4 weeks from germination for male plants, and 4-6 weeks from germination for female plants.
Cannabis Pre-Flowers Are Small Versions of Adult Flowers. These reveal a plant’s sex.
Knowing the plant’s sex is helpful because most hobbyist cannabis growers would like to identify and remove male plants from the grow room early in the growing process. This is because only female plants make potent buds/flowers, while male cannabis plants make non-potent pollen sacs where female plants would grow buds. Additionally, female buds need to avoid pollen from male plants in order to make the highest quality cannabis (sinsemilla or “no seeds”).
Cannabis pre-flowers appear at the base of leaves when male plants are about 3-4 weeks old, and female plants are 4-6 weeks old.
Even if you’re not 100% sure about every plant from looking at the pre-flowers, it’s nice to know which plants you need to watch closely and which are definitely female. However, if precision is very important…
Chemical Leaf Tests Can Determine Sex & Potency for plants as young as 1-3 weeks
Chemical leaf testing is getting less expensive every day and can be used on cannabis seedlings with just a few sets of leaves to test for sex and future potency.
These tests only require a tiny amount of plant tissue (for example a small punch-out from a leaf, or a single cotyledon leaf), so it won’t hurt or slow down your seedlings to take a test sample!
In general, the tests are available for seedlings as young as 1-3 weeks. Sex testing uses a real-time polymerase chain reaction (qPCR) test, and potency tests use Gas Chromatography with a Flame Ionization Detector (GC/FID) or High-Pressure Liquid Chromatography with a Diode Array Detector (HPLC) for testing.
Although testing can be done as early as week 1 from germination, waiting until week 3 to conduct testing on seedlings can increase accuracy, and some companies won’t conduct testing until week 3.
There are many reasons growers would like to know plant sex as early as possible, as well as be able to estimate the overall THC/CBD ratios of future buds!
Did You Know? There are Chemical Leaf Tests that Can Definitively Determine Both Plant Sex & Future Cannabinoid Ratios of Very Young Marijuana Seedlings!
But for those of us using our eyes…
(these turn into buds)
This female pre-flower hasn’t released a wispy white pistil quite yet
When starting with “feminized” seeds (which you can usually only get from a breeder), all your seeds should end up being female, so determining male from female isn’t very important. Learn more about buying seeds (including feminized seeds) from breeders online.
But for growers starting with “regular” (non-feminized) seeds, about half of the plants can turn out to be male. And unfortunately, there’s no way to look at a seed and be able to tell what sex it is.
Unfortunately, you can’t tell a cannabis plant’s sex for sure by looking at the seeds
How to Figure out Sex of a Cannabis Plant by Examining Pre-flowers
Vegetating plants usually reveal their sex when they’re just 3-6 weeks old from seed, but you have to know where to look.
What you’re looking for is “pre-flowers.” These are tiny versions of adult sex parts, and when you see them you can tell what sex the plant is going to be. They usually show up in the upper parts of the plant, closer to the lights, but sometimes you’ll search the whole plant and only find a pre-flower on a random branch lower down on the plant.
Vegetating cannabis plants reveal their sex with “pre-flowers” that usually appear 3-6 weeks from when the plant first germinated.
Although these are the general shapes of male and female pre-flowers, if you continue looking through the pictures below, you’ll see there’s quite a bit of variation on what pre-flowers look like from strain to strain.
Most male plants have grown a pre-flower by week 3-4 from seed, while female plants don’t show until week 4-6. Basically, all vegetative plants will have revealed their sex by about the 6th week from seed.
So, without further ado, here are pictures showing what you’re looking for when it comes to pre-flowers. Remember, pre-flowers are found at the V where stems meet a main stalk. But pre-flowers don’t usually show up all over the plant. Make sure to look around in different places, especially near the top of the plant and closer to the lights
Note: Pre-flowers show up most often near the top of the plant and closer to the lights but could be anywhere on the plant. There may be just one on the whole plant so you may have to search all over!
Male pre-flowers tend to have a “spade” shape, like the spades from a deck of playing cards. Male cannabis plants often (but not always) reveal their sex sooner than female plants.
Male pre-flowers tend to be shaped somewhat like a spade
This male plant was only 3 weeks when it made its first pre-flower. Notice how tiny it is compared to the giant-sized thumb! Often it’s unclear what the sex is when a pre-flower is this small (unless you’ve got a lot of experience) so if you’re not sure, it’s a good idea to wait and see how it develops, just in case.
Just to give you an idea how small these can be when they show up…
This is the exact same picture as above, but with the pre-flower made bigger so you can see it. Pretty tiny, isn’t it?
Male pre-flowers are basically immature pollen sacs. When the plant starts flowering, they will grow and turn into bunches that almost look like grapes.
I’ve also noticed that sometimes (though not always!) the stipules on male plants seem more “leafy” and less “pointy” than stipules on female plants (the stipules are the green hair-like growths near where pre-flowers show up). However, this is just a generality, and should be used together with other factors to determine if a plant is male! There are definitely male plants with pointy stipules and vice versa, but it’s sort of a general difference.
This particular pre-flower is really tough to determine. However, in the end, it was a male plant. The little “stem” is one clue it may be male
Just like the above male plant, sometimes you get almost what looks like two tiny little leaves that the pre-flower pollen sac “unfurls” from. In the above picture the pollen sac is still mostly hidden, while in this next picture, the tiny growths have opened up to fully reveal the pollen sac. This can be confusing because these extra growths don’t appear on all plants, and are not a pre-flower or a stipule.
Here’s another male pollen sac pre-flower that’s on a little “stem”
A single male pre-flower appears
Once you see multiple pollen sacs and no white pistils, you can be confident it’s a male plant
Although this plant ended up being male, the stipules are long, pointy and crossed as you’d normally see with a female plant. That’s why you need to confirm sex with the pre-flowers and not just look at other factors on the plant!
Sometimes the pollen sacs look a little unusual when they first start growing in, but you know it’s male when you see several pre-flowers without any pistils stacked on top of each other like bunches of grapes
If you click the following picture and zoom in close, you can see pollen sacs scattered among the leaves
This is what male pollen sacs look like when the plant actually starts flowering
This male cannabis plant has gotten further along in the flowering stage
This is what a male plant looks like at maturity when it’s starting to spill its pollen
Another example of pollen spilling onto a nearby leaf
For those who’ve never seen a male cannabis plant in its full glory
Ok, now that you know what male pre-flowers look like, what do female pre-flowers look like?
Female pre-flowers tend to be longer and narrower than male pre-flowers, sometimes with a fat bottom. They also usually (but not always) have 1-2 white hairs (pistils) sticking out from the top. Sometimes it takes a few extra days for the pistils to appear.
Wispy white pistils are a sure sign that you’re looking at female pre-flowers
This pre-flower doesn’t have a pistil sticking out at first, but the shape helps tell you it’s a female plant. If you’re not sure about sex after spotting a pre-flower, it’s a good idea to wait and see for a little while, just to see if a white hair appears (which means it’s definitely a girl)
Another example of female cannabis pre-flowers that haven’t revealed their pistil yet
Here’s a picture that shows a pistil right as it’s emerging from the calyx!
If the pre-flower is very pointy and thin like this one on the right, it is often a female pre-flower
Some of the time the stipules (green hair-like growths near where pre-flowers show up) will cross each other on female plants. This certainly doesn’t always happen, as you can see from the pics of female pre-flowers on this page, but while girls can go either way, male plants rarely have stipules that cross each other. So although crossed stipules cannot be used definitively as a way to identify female plants, it can be a small clue to help guide you when you’re not sure. For example, the following female pre-flower doesn’t have a pistil, but the long thin shape combined with the crossed stipules help indicate that this plant is a girl. Whenever in doubt, wait a week and look again!
This female plant has a long, thin calyx and crossed stipules, which are typical female plant features
In this pic, you can see white pistils emerging from the calyxes. Female pistils are white and wispy, never green.
Here’s another female pre-flower that doesn’t have a white hair yet, but you can tell it’s female because it’s long and narrow, instead of spade-shaped
One last female pre-flower without a pistil yet. The long narrow shape is the only thing that gives the sex away until pistils begin to emerge
Super close-up picture of a female cannabis pre-flower
Female cannabis calyxes with pistils, under an LED grow light
Did you know that pre-flowers/calyxes/flowers are actually what holds seeds if your plant gets pollinated? Once pollen touches the white pistils, the pollen gets delivered to the inside and a seed starts forming!
Variability of Cannabis Plant Sex – How to Increase Ratio of Female Plants with Regular Seeds
In fact, to this day scientists are still not sure exactly what causes certain plants to be one sex or another after sprouting. We’ve identified several factors that predict the overall likelihood of male/female plants (for example feminized seeds always produce female plants no matter what), but sex seems to be somewhat fluid in cannabis plants when they’re first germinated.
Certain conditions such as excessive heat, stress, unusual light periods and nutrient problems can cause a greater percentage of plants to produce male flowers.
You may be able to increase the percentage of female plants with regular seeds during the first few weeks of life
On the flip side, the following factors may possibly increase the ratio of female plants with regular seeds (learn more):
- Healthy Mom – Only grow seeds from a vigorous, healthy mother plant who never showed any signs of herming or male pollen sacs (seeds are more likely to grow pollen sacs if the mom plant had a tough start in life, or hermed during the flowering stage)
- Cool Temperatures – Give seedlings slightly cool temperatures (65-75°F day and night) and avoid excessive heat
- High Humidity (50-70% RH)
- Short but not too short days. Keep consistent day and night periods with no light interruptions at night, and days should be 14-18 hours long (between 14/10 and 18/6) for the first few weeks
- Blue light. Always start seeds under a vegetative grow light (something with plenty of blue like a Metal Halide or a 6500k CFL/T5/fluorescent)
- Avoid Deficiencies – Make sure to provide plenty of Nitrogen and don’t let seedlings become nutrient-starved or run into other types of deficiencies
- Prevent Stress, especially heat or light stress during the first few weeks
- Happy Roots – Avoid over (and especially) under watering
Once a cannabis plant is about 3 weeks old, its sex is pretty much completely set and can be determined either by visual inspection or by chemical leaf test.
Unfortunately, due to the fact that different environmental conditions during the first part of life can alter the sex, you can’t look at seeds and definitively know one way or the other whether the plant will end up being female because even the plant doesn’t necessarily “know”.
For example, say you take a clone of a seedling before it’s 3 weeks old. It’s possible that one clone will be male, and the other clone will be female. However, if you take a clone after week 3, the sexes of clones will always match each other. This is further evidence to indicate that the environment can affect sex expression in some cases.